Francis J. Degnan
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I. Topic Area
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Gravity
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II. Start Off Statement
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Using a series of demonstrations we will explore invisible forces that surround us.
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III. Science Processes
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a. observation
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b. prediction
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IV. Materials
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3x5 card, empty jar, water, meter stick, news paper, spherical shapes, hammer
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V. Question To Ask
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What do you think will happen?
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VI. Behind The Events
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The demonstrations should leave the class wondering what is was that they have seen. The visible outcomes seem contrary to common sense. Use these outcomes to lead to discussion.
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a. The upside down glass
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Air exerts pressure in all directions, holding the cardboard on the bottom of the jar. Yes it even pushes up!
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b. Newspaper punch
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The pressure of air at sea level is roughly 14.7 pounds per square inch. This dramatically shows the 9,055.5 pounds that are on a piece of paper 22”x24”.
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c. The Ball Drop
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Here we must stress that gravity acts with the same force on on all objects, no matter what the size or mass. A very important thing to do is to drop the spheres at exactly the same time.
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VII. Procedure
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a. Gather all the materials
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b. Be sure each student has a Guess What sheet. Be sure the student fills in the column for their prediction.
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c. Do these activities as a teacher demonstration with student helpers. Do the experiments as many times as needed so that the students have time to formulate some idea of what took place.
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VIII. Discussion
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a. If gravity is responsible for our weight on this planet, what would we weigh on other planets?
III. Gases
The intent of student activity sheet 2,
Now
What?
is to get the elementary children thinking about their environment. The wondrous qualities of the gases that surround them are not usually realized. A discussion to begin this investigation could pose the questions, “When is a room empty? . . . Is it empty when all the children have left? . . . Is it empty if all the furniture is removed?” The inference to be drawn is that unless somehow the air is removed the room is never empty. This clear stuff that sound travels through, that surrounds us, and that is necessary for our very existence is everywhere in our environment. Activity A shows the students that air offers resistance to the sheet of paper. The sheets of paper were identical, but once crumpled, one falls at a much greater speed. The students may recall that on activity sheet 1 the objects fell at the same speed regardless of their size and weight, but their spherical shapes offered little resistance to the air. In fact it was stipulated that objects fall at the same rate if there is little or no air resistance. Elementary students may be aware of the term vacuum, a space from which the air has been removed. If the sheets of paper were dropped in a vacuum they would fall at the same rate.
Extensions of this section of the lesson that could be considered might include the following. The observation that air not only offers resistance but also exerts force. Fans move air for us on hot days, gentle breezes set leaves in motion and sailboats are pushed gracefully along, these scenarios and others could be brainstormed in discussion. A discussion could study the composition of the air in our atmosphere. Specific gases, their symbols and their characteristics could be mini research projects.
Activities B, C and D show that Gases can be compressed, can be expanded by heating and can even be present in liquids. These properties are amazing! Balloons, tires, floats and balls of many shapes and sizes are blown up, that is air is compressed into them. Compressed oxygen helps the ill as well as the welder and the diver uses compressed air to dive beneath the sea. Sport balloonists depend upon compressed gases to heat and expand the air for their vehicles. Rising columns of air heated by the earth’s surface allow birds and glider pilots to soar. If enough air is heated it may become a low pressure area on our weather map. Finally if rushing streams and slapping waves didn’t absorb oxygen what would happen to the fish and other creatures of the sea? In addition don’t forget our favorite beverages. The bubbles in the carbonated drinks do come out of the liquid. In the final activity if a balloon is put over the top of the seltzer bottle it inflates, making the presence of the gas more concrete to the young learner.
Now What?
(figure available in print form)
